A wireless communication system typically includes a base station in wireless communication with a plurality of user devices (which may also be referred to as mobile stations, subscriber units, access terminals, etc.). The base station transmits data to the user devices over a radio frequency (RF) communication channel. The term “downlink” refers to transmission from a base station to a user device, while the term “uplink” refers to transmission from a user device to a base station.
Orthogonal frequency division multiplexing (OFDM) is a modulation and multiple-access technique whereby the transmission band of a communication channel is divided into a number of equally spaced sub-bands. A sub-carrier carrying a portion of the user information is transmitted in each sub-band, and every sub-carrier is orthogonal with every other sub-carrier. Sub-carriers are sometimes referred to as “tones.” OFDM enables the creation of a very flexible system architecture that can be used efficiently for a wide range of services, including voice and data. OFDM is sometimes referred to as discrete multi-tone transmission (DMT).
The 3rd Generation Partnership Project (3GPP) is a collaboration of standards organizations throughout the world. The goal of 3GPP is to make a globally applicable third generation (3G) mobile phone system specification within the scope of the IMT-2000 (International Mobile Telecommunications-2000) standard as defined by the International Telecommunication Union. The 3GPP Long Term Evolution (“LTE”) Committee is considering OFDM as well as OFDM/OQAM (Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation), as a method for downlink transmission, as well as OFDM transmission on the uplink.
Wireless communications systems (e.g., Time Division Multiple Access (TDMA), Orthogonal Frequency-Division Multiplexing (OFDM)) usually calculate an estimation of a channel impulse response between the antennas of a user device and the antennas of a base station for coherent receiving. Channel estimation may involve transmitting known reference signals that are multiplexed with the data. Reference signals may include a single frequency and are transmitted over the communication systems for supervisory, control, equalization, continuity, synchronization, etc. Wireless communication systems may include one or more mobile stations and one or more base stations that each transmits a reference signal. In addition, wireless communication systems may transmit channel quality information (CQI), acknowledgment reports (ACK) and negative acknowledgment reports (NAK). The CQI and the ACK/NAK may be modulated (or covered) by a sequence that ideally orthogonalizes the CQI and the ACK/NAK. However, covered CQI and ACK/NAK from other systems may introduce interference. As such, benefits may be realized from systems and methods that design a sequence for code modulation of data as well as channel estimation.
Moreover, some conventional arts related to the present invention are disclosed in the following non-patent documents:
Sharp, “Optimized UL RS Design, and some issues with current UL RS proposals”, 3GPP TSG-RAN WG1 #48bis R1-071494, Mar. 30, 2007.
Sharp, “Optimized UL RS Design-OZCL Sequences”, 3GPP TSG-RAN WG1 #48bis R1-072053, May 11, 2007.
Texas Instruments, “ACK/NAK and CQI Multiplexing and Performance in E-UTRA UL”, 3GPP TSG RAN WG1 #49 R1-072206, May 11, 2007.
DILIP V SARWATE, “Bounds on Crosscorrelation and Autocorrelation of Sequences”, November 1979, IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. IT-25, NO. 6, pp. 720-724.